The present invention relates to a semiconductor device, and more particularly, to an impedance-controlled pseudo-open drain output driver circuit and a method for driving the same.
An output driver circuit is an interface circuit to drive an output pad (DQ), to which a predetermined load is connected, so as to output an internal data of a semiconductor device to an external circuit.
A pseudo-open drain driver is an interface circuit adopted as a standard in Graphics Double Data Rate 3 (GDDR3). While a push-pull driver is based on a current, a pseudo-open drain driver is based on a voltage.
To control an output impedance, a conventional pseudo-open drain output driver circuit repeats a process of changing an impedance code of an output driver circuit using an external resistor having a desired output impedance until the output impedance is equal to the output impedance. The pseudo-open drain output driver circuit can serve as an output driver circuit only when the output impedance is determined after the closed-loop process is completed.
However, the conventional pseudo-open drain output driver circuit is not suitable for high-speed operation because a locking time is long and inconstant. In addition, error may occur when the resistance is matched at the outside.